Effect of Sterile Boll Weevils (Coleoptera: Curculionidae) and Insecticide in Isolated Small Plots in Florida

Abstract

In the spring and summer of 1989, insecticide and sterile boll weevils, Anthonomus grandis Boheman, were applied to plots of cotton on two private research farms at Vero Beach, Florida to suppress the native boll weevil population. Plots were treated weekly with azinphosmethyl followed by the release of about 500 sterile boll weevils per acre two days later. Egg hatch was 5% on the Mobay farm where serially planted plots of cotton were destroyed soon after blooming. On the Ciba-Geigy farm egg hatch averaged 32% prior to the formation of bolls 2.5 cm (1 in.) or larger in diameter and 77% when bolls were larger than 2.5 cm in diameter. Normally, egg hatch in fields with no sterile weevils is about 94% so their effect in preventing or significantly lowering the reproductive activity of native females entering the cotton fields was demonstrated. After natives began emerging from the clumped areas where oviposition had taken place, the effectiveness of the sterile weevils was significantly diminished.The Ciba-Geigy research farm had received more than 30 applications of azinphosmethyl during the 1988 growing season, and the Mobay farm had received 6 applications of methomyl. In 1989, 16 pheromone baited traps placed around the perimeter of each farm in 1989 captured an average of 12 (Mobay) and 37 (Ciba-Geigy native weevils per week before and during the treatment period. At Ciba-Geigy 41% of the trapped weevils were sterile compared to 34% at Mobay. In 1990, 16 pheromone traps placed around the Mobay and Ciba-Geigy farms averaged 0 and 4 weevils per week, respectively, during the growing season.